So I did some digging and apparently the command is still there. The command is:
ioreg -lw0 | grep \"EDID\" sed "/[^<]/s///" | xxd - -r | strings -6
More info as to what the numbers mean:
https://forums.macrumors.com/threads/only-early-2013-rmbp-15-lcd-model-ir-test.1567570/
Retina test is available here:
https://github.com/mitchmalone/retina-test
I have switched the screens on the MacBook Pros and I started getting headache from the one that came in so it seems to be a panel problem.
The one that I bought (now with the panel that I have been using forever and was able to use with no problems) is LP154WT1-SJA2
The one that I was able to use (and now with the panel from the newer MacBook Pro that gives me eyestrain) is LP154WT1-SJA1
I'm not sure how the ioreg command works, but I suspect it queries system information and doesn't query the actual panel itself which means SJA1 is the one that doesn't give me eyestrain and SJA2 is the one that does. I will switch the panels over again to verify this.